1. Field of the Disclosure
The disclosure relates generally to micromechanical devices or micro-electromechanical systems (MEMS) and, more particularly, to micromechanical or MEMS resonators.
2. Brief Description of Related Technology
Surface micromachining is one of the mainstream fabrication processes for MEMS resonators. Surface micromachining produces devices capable of low voltage operation (e.g., due to small, well controlled gaps), with a smaller resonator size (e.g., typically 20-50 times smaller than other MEMS resonators) and at a lower manufacturing cost (e.g., an expensive silicon-on-insulator (SOI) substrate may be avoided). The devices are also compatible with various types of wafer level packaging processes, such as glass frit, eutectic bonding, and silicon-fusion bonding.
However, the simplicity of surface micromachining leads to MEMS resonators that are more difficult to mechanically compensate for temperature-based shifts of the resonant frequency of the resonator device. The resonant frequency of a typical surface micromachined resonator has a temperature coefficient of frequency of about −20 ppm/° C. over an operating temperature range from, for instance, about −40° C. to about 85° C. Attempts at mechanical temperature compensation to address such temperature-based frequency instability have been described in Hsu, et al., “Mechanically Temperature-Compensated Flexural-Mode Micromechanical Resonators,” Technical Digest, IEEE International Electron Device Meeting (IEDM), pp. 399-402 (2000), and Hsu et al., “Stiffness-compensated temperature-insensitive micromechanical resonators”, Technical Digest, IEEE MEMS Conference, pp. 731-734 (2002), the entire disclosures of which are hereby incorporated by reference.